Vent for a hydraulic drive device

ABSTRACT

A vent for a hydraulic drive device disposed in a housing includes a vent body having a closed first side, a second side having an opening, and a sidewall. An internal passageway in the vent body connects the second side opening to the atmosphere. The vent body is removably disposed in a vent opening in one of two positions. When the first side of the vent body is inserted into the vent opening, the closed first side prevents communication between the sump and atmosphere, and when the second side of the vent body is inserted into the vent opening, the internal passageway and the second side opening permit communication between the internal sump and atmosphere.

CROSS REFERENCE

This application is a continuation of U.S. patent application Ser. No.14/828,078, filed on Aug. 17, 2015, which is a continuation of U.S.patent application Ser. No. 13/913,893, filed on Jun. 10, 2013, which isa divisional of U.S. patent application Ser. No. 12/533,871, filed onJul. 31, 2009, now U.S. Pat. No. 8,464,610, which claims the priority ofU.S. Provisional Patent App. No. 61/085,612, filed on Aug. 1, 2008. Theterms of these prior applications are incorporated herein by referencein their entirety.

BACKGROUND OF THE INVENTION

This application is related to drive devices for a variety of vehicles.

SUMMARY OF THE INVENTION

The present invention provides a drive device for a variety of vehicles.

A better understanding of the properties of the invention will beobtained from the following detailed description and accompanyingdrawings which set forth one or more illustrative embodiments and areindicative of the various ways in which the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of a hydraulic drivedevice in accordance with the present invention.

FIG. 2 is a perspective view of the hydraulic drive device shown in FIG.1 with the housings removed.

FIG. 3 is a perspective view of the portion of the hydraulic drivedevice shown in FIG. 1 with certain items removed for clarity.

FIG. 4 is an opposite perspective view of the portion of the hydraulicdrive device shown in FIG. 3, with certain items removed for clarity.

FIG. 5 is a perspective view of the portion of the hydraulic drivedevice shown in FIG. 4 with the reduction gear set removed.

FIG. 6 is an opposite perspective view of the portion of the hydraulicdrive device shown in FIG. 5 with the filter removed and a shock valveassembly shown in exploded format.

FIG. 7 is a perspective view of the portion of the hydraulic drivedevice shown in FIG. 6 rotated 90 degrees clockwise.

FIG. 8 is a perspective view of the portion of the hydraulic drivedevice shown in FIG. 7 with the assembled clutch and certain otherelements shown exploded format.

FIG. 9 is an exploded perspective view of the clutch assembly of thehydraulic drive device shown in FIG. 1.

FIG. 10 is an exploded perspective view of the center section, clutchactuators, pinion gear and wear washer of the hydraulic drive deviceshown FIG. 1.

FIG. 11 is an elevational view of the hydraulic cylinder block runningsurfaces side of the center section of the hydraulic drive device shownin FIG. 1.

FIG. 12 is an elevational view of the reverse side of the center sectionshown in FIG. 11.

FIG. 13 is a top plan view of the center section shown in FIG. 11 alongthe lines 13-13.

FIG. 14 is a bottom plan view of the center section shown in FIG. 12along the lines 14-14.

FIG. 15 is an elevational view of a second embodiment of a centersection.

FIG. 16 is a bottom plan view of the center section shown in FIG. 15along the lines 16-16 of FIG. 15.

FIG. 17 is a cross-sectional view of the center section shown in FIG.15, along the lines 17-17 of FIG. 15.

FIG. 18 is a cross-sectional view of the center section shown in FIG.15, along the lines 18-18 of FIG. 16.

FIG. 19 is an exploded view of the second housing and one of the axlesupport housings.

FIG. 20 is a perspective view of a vent in accordance with theprinciples of the present invention.

FIG. 21 is a side elevational view of the vent shown in FIG. 20.

FIG. 22 is a sectional view along the lines 22-22 of FIG. 21.

DETAILED DESCRIPTION OF THE DRAWINGS

The description that follows describes, illustrates and exemplifies oneor more particular embodiments of the present invention in accordancewith its principles. This description is not provided to limit theinvention to the embodiment or embodiments described herein, but ratherto explain and teach the principles of the invention in such a way toenable one of ordinary skill in the art to understand these principlesand, with that understanding, be able to apply them to practice not onlythe embodiment or embodiments described herein, but also otherembodiments that may come to mind in accordance with these principles.The scope of the present invention is intended to cover all suchembodiments that may fall within the scope of the appended claims,either literally or under the doctrine of equivalents.

The embodiments of drive device 16 disclosed herein may be used in avariety of vehicles such as a walk-behind snow thrower or other suchvehicles. However, the embodiments disclosed herein are not limited touse in this type of vehicle.

Drive device 16 is depicted in detail in FIGS. 1-14. Drive device 16 isshown as a type of continuously variable hydraulic or hydrostatictransmission of a type known as an integrated hydrostatic transmission.Such transmissions are well known in the art and will only generally bedescribed herein. Moreover, it will be appreciated by those in the artthat the scope of the present invention is not limited to hydraulictransmissions, but may include any type of continuously variabletransmission.

Drive device 16 is powered by a prime mover (not shown), and, in thedepicted embodiment, drives input shaft 34 by way of a belt and pulleysystem. For convenience, only pulley 32 of the belt and pulley system isshown. Input shaft 34 is engaged to and drives hydraulic pump 36, whichis rotatably disposed on pump running surface 163 of center section 38.Motor 40 is rotatably disposed on motor running surface 164, formed onmotor mounting portion 174. Hydraulic pump 36 is hydraulically connectedto motor 40 through internal porting 165, which is formed in centersection 38 and connects pump running surface 163, formed on pumpmounting portion 175, with motor running surface 164.

Center section 38 may have a plurality of other components installedtherein or thereon to aid in the operation of drive device 16, such asvalves 42 (seen, for example, in FIG. 6) that may comprise check valves,combination valves that include check, neutral, pressure rise rate, orrelief functions, bypass valves or other types of valves. Valves 42 mayeach comprise a seat or body 43 that is pressed into a port in centersection 38 that communicates with internal porting 165 of center section38. Depending on the operating conditions of drive device 16, additionalretention of body 43 may be provided. Thus, center section 38 may beconfigured to permit staking of body 43 in place, or a retaining ring(not shown) or other element may be located adjacent body 43 to keep thepressure conditions of the internal porting of center section 38 frompushing body 43 out of center section 38.

As shown in FIG. 6, center section 38 may also include one or more shockvalves 170. In the depicted embodiment, shock valves 170 comprise a ball171 and spring 172, both of which are installed in pocket 150 andretained with cotter pin 173, installed through openings 152. As isknown in the art, the purpose of this type of valve is to prevent systemfluid pressure spikes from causing damage to moving parts interfaces,such as gears, bearings or cylinder block running faces. By way ofexample, and in no way limiting, a pressure spike may cause hydraulicpump 36 or hydraulic motor 40 to temporarily lift off from centersection 38, possibly causing damage to pump running face 163 or motorrunning face 164. In an application such as a walk-behind snow thrower,this kind of pressure spike is much more likely to occur when drivingthe snow thrower forward into heavy snow or against an obstruction, andis unlikely to occur during reverse operation. Thus, under certainoperating conditions, only one shock valve 170 may be required, whichwould be placed on the fluid side of the hydraulic circuit that is underhigh pressure when the vehicle is operating in the forward direction.

Other elements located on or in center section 38 may include filter 44and fasteners 50. As seen, for example, in FIG. 3, fasteners 50 extendparallel to shaft 34 and shaft 48 to support center section 38 in a sump(not shown) formed by first housing 52 and second housing 54. Note thatsuch center section and fastener configurations are known in the art.For example, U.S. Pat. No. 5,392,670 to Hauser, incorporated herein byreference in its entirety, shows a center section 62 installed within ahousing element. Unnumbered fasteners holding center section 62 to ahousing element are readily seen in FIGS. 1, 3 and 5 of the '670 patent.A person of skill in the art would recognize that similar fasteners holdcenter section 62 to a housing element in FIG. 6 of the '670 patent.

A swash plate such as swash plate 56 is provided to control thedisplacement of pump 36. Thus, as swash plate 56 is moved by trunnionarm 58, the displacement of pump pistons 35 in pump 36 changes, causingfluid to flow through the internal porting 165 of center section 38 tomotor 40, causing motor 40 to rotate. Trunnion arm 58 may be movedmanually by a control arm 59 or by an electronic or hydraulic control,as is known in the art. Examples of electronic controls that could beused in connection with the present invention may be found in U.S. Pat.No. 7,073,330 and Pub. No. 2008/0018269, both of which are commonlyowned with this invention and incorporated herein by reference in theirentireties.

Motor 40 drives output shaft 48. As shown in FIG. 4, output shaft 48 hasa pinion bevel gear 60 mounted thereon. Output shaft 48 passes throughand is supported by opening 144 in center section 38. The end of shaft48 opposite bevel gear 60 is supported by housing 52 and may include athrust washer or disc (not shown) installed in shaft support 53 ofhousing 52 to prevent excessive wear to housing 52. As shown in FIG. 10,pinion gear 60 may rotate on wear washer 65 to prevent excessive wear tocenter section 38.

As output shaft 48 rotates, pinion gear 60 drives clutch gear 62.Located on either side of clutch gear 62 are rings 86, which are part ofclutch assembly 61, the operation of which is described in detail below.As a preliminary matter, both rings 86 are biased by springs 80 to theengaged position, and an arm 72, in conjunction with a fork 106, ispositioned proximate to each ring 86, and may rotate to move rings 86 tothe disengaged position, independent of one another. Each ring 86 isassociated with one of shafts 68 or 70 through a separate gear train. Byallowing for individual engagement and disengagement of the rings 86,individual control of shafts 68 and 70 may be provided, allowing drivedevice 16 to both steer and propel a vehicle comprising drive device 16.

As stated above, steering of a vehicle is accomplished by use of clutchassembly 61, which is shown in detail in FIGS. 7-9.

In FIGS. 4-7, both rings 86 of clutch assembly 61 are shown in theengaged position. In this position, clutch gear 62 provides motive powerto rotate both flange gears 90. Each flange gear 90 is, in turn, engagedto a reduction gear set 100, as seen, for example, in FIG. 4. In thedepicted embodiment, each reduction gear set 100 includes a reductionspur gear 101 and a spur gear 104. Each spur gear 104 is connected toone of axle shaft 68 or 70 by splines 110.

Jack shaft 102 supports the pair of reduction spur gears 101. Cuppedwashers 103 are used near each end of jack shaft 102 to prevent the hubsof gears 101 from cutting into housing 54. Jack shaft 102 is retained byplugs 57 installed in each side of housing 54.

As shown in FIG. 9, clutch 61 includes a centrally located clutch gear62, which includes a bevel gear portion 63, which is driven by pinionbevel gear 60 whenever the prime mover is operating and providing inputto drive device 16, and trunnion arm 58 is rotated out of the neutralband in either a forward or reverse direction. For purposes of thisdescription, the neutral band is defined as a pump displacement zone ator near zero displacement in which motive force provided by pump 40 andmotor 36 is not sufficient to cause rotation of axle 68 or 70 duringnormal vehicle operating conditions.

Rings 86 are engaged to bevel gear 62 such that each ring 86 rotateswhenever gear 62 rotates. When a ring 86 is engaged with a flange gear90, spur gear portion 91 of gear 90 drives its related reduction spurgear 101, which drives its related spur gear 104, thereby rotating axle68 or 70, respectively.

As best shown in FIGS. 7-9, each ring 86 is biased toward engagementwith its respective mating flange gear 90 by the force of a plurality ofsprings 80, each located in an opening 82 of housing portion 64 ofclutch gear 62. In order to remove the motive force from one or both ofaxles 68 or 70, an arm 72 is rotated by the vehicle operator. Becausefork 106, which comprises tines 108, is splined to arm 72, rotation ofarm 72 causes the tines 108 to engage the respective ring 86, movingring 86 away from its respective flange gear 90. This movement causesprotrusions 94 of ring 86 to disengage from recesses 96 formed in flangeportion 92 of flange gears 90, thereby disconnecting the driving forcefrom flange gear 90.

Simultaneous contact of both ends of all springs 80 is continuouslymaintained with surfaces 84 of protrusions 88 on rings 86. Protrusions88 formed on rings 86 slidingly engage slots 82 and retain springs 80within the fully enclosed portion of slots 82. Space is provided in theinterface between slots 82 and protrusions 88 to allow fluid to flowfreely through slots 82 when one or both rings 88 are pushed toward gearportion 63.

Clutch support shaft 67 is installed through openings 140 in arms 161 ofcenter section 38. Clutch assembly 61 is rotatably mounted on shaft 67,which may be identical to jack shaft 102. Inner surfaces of arms 161 maybe machined to ensure correct spacing of clutch 61 components andpreload on springs 80. Wear washers 99 located adjacent to innersurfaces of arms 161 interface with grooved outer end surfaces 98 ofgears 90. Grooves in surfaces 98 ensure adequate lubrication of thesemating surfaces, which are pushed into rotating contact with one anotherby forces applied by springs 80 and transferred through rings 86. Innerend surfaces 97 of gears 90 are also grooved, since they come intorotating contact with end surfaces 69 of gear 62.

Once force is removed from handle 72, or alternatively, if handle 72 isreturned to its original position, springs 80 will then act on surfaces84 to slide ring 86 toward gear 90, thus permitting protrusions 94 toreengage recesses 96. Since rings 86 are continuously driven by gear 62,reengagement of protrusions 94 with recesses 96 in gears 90 will causeaxle shaft 68 or 70 to rotate.

It will be appreciated by those in the art that recesses 96 of gears 90are larger than protrusions 94 of rings 86. This sizing is necessary toensure clutch engagement when rings 86 are rotating and gears 90 are notrotating or are rotating more slowly than rings 86.

If both arms 72 are rotated out of their original positions at the sametime, neither axle will be driven. If both arms 72 are returned to theiroriginal positions, both axles will be driven. If only one arm 72 isrotated out of its original position, only its associated axle will bedrivingly disconnected, causing the vehicle to turn.

Arm 72 interfaces with fork 106 by way of splines 71. The relativelylarge size of these elements allows distribution of stresses over alarge area, permitting plastic to be used for both handle 72 and fork106.

A first embodiment of center section 38 is shown in detail in, e.g.,FIGS. 2-8 and 10-14. Pump input shaft 34, motor output shaft 48 andclutch actuator arms 72 are all partially supported by center section38. Opening 146 supports one end of shaft 34, while opening 144 supportsone end of shaft 48. Openings 142 support ends 143 of arms 72 which, inturn, support actuator forks 106. Clutch 61 is entirely supported onshaft 67 which is installed through openings 140 in clutch support arms161 of center section 38.

In order to provide a strong and rigid center section, a diamond-shapedmounting pattern is utilized in conjunction with a diamond-shapedreinforcement rib pattern. Four fasteners 50 are inserted throughopenings 148 to secure center section 38 to housing 52, providing arigid subassembly of these components. A central strengthening rib 162and four additional ribs 166 form a double triangular pattern within anoverall diamond pattern. Specifically, as seen in FIG. 11, two ribs 166extend from proximate an opening 148 to motor mounting portion 174, andtwo ribs 166 extend from proximate an opening 148 to pump mountingportion 175. This double triangular pattern serves to structurallyisolate running faces 163 and 164 from one another and from stressestransferred from clutch 61. Specifically, as will be obvious to those inthe art, the axes of rotation of pump 36 and motor 40 define a firstplane, and central strengthening rib 162 is disposed perpendicular tothat first plane. Note that three fasteners arranged in a surroundingtriangular pattern are associated with each running face. Fluid passagestructures 167 and 168, in combination with central rib 162 andbuttressing ribs 176 and 178, form a sturdy H-shaped central structureto further strengthen, stiffen, and help maintain flatness of centersection 38. Finally, because of the support provided by the H-shapedcentral structure and the overall diamond pattern, center section 38 canbe manufactured with significantly less material than other centersections. By way of example, center section 38 comprises several areas501 to 510 that either lack any material, or have a substantiallyreduced amount of material. By way of example, in the depictedembodiment, a thin webbing of material separates area 501 from area 510,area 502 from area 509 and area 507 from area 508. It will beappreciated by those in the art that this thin webbing may be removed,thus making areas 501 and 510, areas 502 and 509 and areas 507 and 508each one space that lacks material.

Easily accessible valve openings 154 are provided for installation ofvalves 42 in center section 38. Filter 44 is easily installed overvalves 42. Central strengthening rib 162 forms one side of pockets 150so that minimal material is used to form pockets 150. Installation ofvalves 170 in pockets 150 is also very simple. Note that push-lock pins(not shown) may be used in lieu of cotter pins 173 to further simplifyassembly of valves 170 by avoiding the cotter pin bending operation. Itwill also be appreciated by those in the art that, when used in certainapplications, valves 170 may not be needed, and, as such, pockets 150may not be included.

A second embodiment of a center section of the present invention isdisclosed in FIGS. 15-18. As seen, center section 238 comprises manyfeatures that are similar to center section 38. Features which aresubstantially similar or identical to those previously described willnot be described in detail, but are designated by similar numerals usingthe initial number “2.” First port 302 and second port 304 can be seenin, e.g., FIG. 18, and are used to fluidly connect a pump, such as pump36, to a motor, such as motor 40. Cross channel 306 may be provided toconnect first port 302 and second port 304.

It is well known in the art that, due to various operating conditions orcircumstances, one side or another in a hydraulic circuit, such as thecircuit displayed in FIG. 18, may experience sudden increases inhydraulic pressure. Cross channel 306 can be used to relieve suchincreases. In the embodiment depicted in FIGS. 17 and 18, valve 310 is ashock valve disposed in cross channel 306. Shock valves are generallywell known in the art and will only briefly be described herein. If thehydraulic pressure in first port 302 increases past a set point, thehydraulic force acting on ball poppet 312 will exceed the force ofspring 314 acting on ball poppet 312, and valve 310 will open to permithydraulic fluid to flow from first port 302, to second port 304,lessening the hydraulic pressure. It will be appreciated by those in theart that, while valve 310 is depicted as a shock valve, other types ofvalves may be located in cross channel 306, depending on the capacity inwhich center section 238 is being used. By way of example only, valve310 may be a combination check valve pressure relief valve, as disclosedin U.S. Pat. No. 7,367,353 which is incorporated herein in its entiretyby reference.

As in the first embodiment, when used in certain applications, somevalves may not be needed, and, as such, pockets 250, as seen in FIG. 16,may be omitted from center section 238.

In a wheeled vehicle application or other application employingrelatively long output shafts, each axle shaft 68 and 70 may requirebearing support some distance from housing 54. Axle support housings 73and 74 may provide locations for bearing support some distance fromsecond housing 54, such as bearing support 75 shown in FIG. 1. Dependingupon the material selected for axle support housings 73 and 74 and theanticipated loading of axles 68 and 70, bearing support 75 may beconfigured as a journal bearing or molded to receive a bushing orbearing. Axle support housings 73 and 74 may also provide fasteneropenings 77 to attach drive device 16 to a vehicle.

Fasteners 79 and openings 77, as depicted in FIG. 1, may also serve tomaintain the orientation between axle support housing 74 and secondhousing 54. As best seen in FIG. 19, and as discussed in detail below,the depicted embodiment of engagement structure 113 comprises aplurality of projections 117, each projection 117 having a slot 118 andbeing separated from the succeeding projection 117 by a gap 116. Supporthousing 74 has a plurality of projections 114 formed thereon. Duringassembly, the plurality of projections 114 are positioned in gaps 116 onsecond housing 54, and axle support housing 74 is rotated so thatprojections 114 engage slots 118, thus securing axle support housing 74to second housing 54. However, axle support housing 74 may still rotatesuch that projections 114 become disengaged from slots 118. When drivedevice 16 is attached to vehicle frame (not shown) by fasteners 79, anda fastener 51 is located in opening 120, as seen, e.g., in FIG. 1, therotation of axle support housing 74 with respect to second housing 54 islimited. Thus, the fasteners that attach drive device 16 to a vehicleframe also act to keep axle support housing 74 attached to drive device16. This arrangement does permit, however, limited movement of axlesupport housing 74 relative to second housing 54 as the vehicle frameflexes in order to reduce the stress in axle support housing 74 undersome load conditions, such as when drive device 16 is installed in avehicle. It should be noted that other locations for fasteners mayalternately be selected depending upon the application of drive device16.

Because axle support housings 73 and 74 are essentially hollow,additional support for axle support housings 73 and 74 may be desirable.As these two axle support housings 73 and 74 are essentially identical,only one will be described. As seen in, e.g., FIG. 19, housing 54 andsupport housing 74 have a plurality of support structures.

Each support structure includes lip 119, formed adjacent projection 117to form groove 115. Edge 121 of axle support housing 74 may then rest ingroove 115 when axle support housing 74 is attached to second housing 54to maintain the shape and position of axle support housing 74. Secondhousing 54 has a plurality of projections 117 and a plurality of lips119. The support for axle support housing 74 may allow axle supporthousing 74 to be formed of aluminum or a plastic. The plastic may be anapproximately 30% glass filled nylon 6/6. In the depicted embodiment,axle support housing 74 comprises a 33% glass filled nylon 6/6. It willbe appreciated by those in the art that under certain conditions, analuminum axle support housing 74 may be cast as a single element withsecond housing 54.

Axle support housing 74 may have additional features. For example,openings 122 serve to reduce the amount of material or debris that maybuild up within axle support housing 74, since axle support housing 74is mated to second housing 54 without sealing. Thus, debris that mightenter axle support housing 74 may either fall through an opening 122located on the bottom of axle support housing 74, or water or othercleaning fluid may be introduced into one of the openings 122 to cleanthe interior of axle support housing 74.

When joined together by a plurality of fasteners 55, first housing 52and second housing 54 form a sump that provides the hydraulic fluid forhydraulic pump 36, hydraulic motor 40 and the other hydraulic elementsof drive device 16. Because the fluid in the sump can expand or contractwith changes in temperature, a vent is typically provided for the sump.

Vent 76, which is preferably of a material that provides a fluid seal,such as rubber, may be seen in more detail in FIGS. 20-22. Vent 76 maybe installed in a hole such as hole 78, and may be installed indifferent orientations; it comprises a first side 180 that prevents airfrom entering or exiting drive device 16, and a second side 182 thatpermits communication between the sump (not shown) and the externalenvironment. First side 180 of vent 76 is installed into drive device 16during shipping, or at other times when leaking of hydraulic fluid is apossibility. Once drive device 16 reaches an original equipmentmanufacturer or other end user, vent 76 is removed from drive device 16and installed again into drive device 16 with second side 182 insertedinto drive device 16. With second side 182 installed in drive device 16,air may be exchanged between the exterior of drive device 16 and theinternal sump of drive device 16 by way of first passage 184 and secondpassage 186, with the direction of air movement dependent on whether thehydraulic fluid within drive device 16 is expanding or contracting. Anair permeable, water impermeable membrane 188 may optionally be includedin vent 76 to minimize the introduction of water or water vapor into theinternal sump.

While a specific embodiment of the invention has been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangement disclosed is meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalent thereof.

What is claimed is:
 1. A drive device comprising: a housing forming aninternal sump, and a vent opening formed in the housing; a centersection disposed in the housing and comprising: a first side and asecond side opposite to the first side, the first side and the secondside being connected by a pair of opposite side edge surfaces; and afirst running surface and a second running surface located on the firstside, wherein the first running surface is connected to the secondrunning surface by hydraulic porting formed internal to the centersection; a pump cylinder block rotatably disposed on the first runningsurface and driven by an input shaft; a vent removably disposed in thevent opening, wherein the vent may be inserted in a first position whichprevents communication between the internal sump and the atmosphere or asecond position which permits communication between the internal sumpand the atmosphere; a control arm disposed external to the housing andengaged to a trunnion arm in the housing for controlling an output ofthe pump cylinder block; a motor cylinder block rotatably disposed onthe second running surface and driving a motor shaft; a clutch mechanismoperatively engaged to the motor shaft; and a first axle and a secondaxle engaged to and driven by the clutch mechanism.
 2. The drive deviceof claim 1, wherein the vent comprises: a vent body having a first ventside and a second vent side, and a vent sidewall extending between thefirst vent side and the second vent side; an extension extending outfrom the vent sidewall between the first vent side and the second ventside; and a passageway comprising a first passage formed in the ventbody and a second passage formed in the extension, wherein the firstpassage is closed at the first vent side and open at the second side toan opening formed in the second vent side, and the second passage has aninternal end open to the first passage and an external end open to theatmosphere.
 3. A drive device comprising: a housing forming an internalsump, the housing comprising a vent opening formed in an externalsurface thereof; a hydraulic drive apparatus disposed in the internalsump and driving at least one output axle; a vent removably disposed inthe vent opening, the vent comprising: a vent body comprising a closedfirst side, a second side having an opening formed therein, and asidewall extending between the first side and the second side; and aninternal passageway comprising: a first passage extending into the ventbody from the opening formed in the second side, the first passageterminating at a point inside the vent body; and a second passage formedgenerally perpendicular to the first passage, wherein the second passagehas an internal end open to the first passage inside the vent body, andan external end open to the atmosphere; wherein the vent body may beinserted in the vent opening in a first position or a second position,whereby when the vent body is in the first position, the first side ofthe vent body is inserted into the vent opening and the vent bodyprevents communication between the internal sump and the atmosphere, andwhen the vent body is in the second position, the second side of thevent body is inserted into the vent opening and the vent body permitscommunication between the internal sump and the atmosphere through theinternal passageway.
 4. The drive device of claim 3, further comprisinga membrane disposed in the internal passageway, wherein the membrane isair permeable and water impermeable.
 5. The drive device of claim 4,wherein the membrane is disposed in the first passage.
 6. The drivedevice of claim 3, wherein the sidewall of the vent body defines a firstdiameter, and a portion of the first side and the second side each havea second diameter that is larger than the first diameter.
 7. The drivedevice of claim 3, wherein the vent further comprises an extensionextending out from the vent body at a point between the first side andthe second side, and the second passage is formed in the extension. 8.The drive device of claim 7, wherein the extension comprises a generallycylindrical extension sidewall connecting a first surface and a secondsurface, wherein the first surface contacts the external surface of thehousing when the first side of the vent body is inserted into the ventopening and the second surface contacts the external surface of thehousing when the second side of the vent body is inserted into the ventopening.
 9. The drive device of claim 8, further comprising a membranedisposed in the internal passageway, wherein the membrane is airpermeable and water impermeable.
 10. The drive device of claim 9,wherein the membrane is disposed in the first passage.
 11. The drivedevice of claim 8, wherein the sidewall of the vent body defines a firstdiameter, and a portion of the first side and the second side each havea second diameter that is larger than the first diameter.
 12. A vent foruse in a hydraulic drive device having a housing forming an internalsump and a vent opening formed in the housing, the vent comprising: avent body having a first side and second side and a vent sidewallextending between the first side and the second side, the vent sidewallbeing cylindrical and having a first diameter; an extension extendingfrom the vent sidewall, the extension having a width that is larger thanthe first diameter; an internal passageway comprising a first passageformed in the vent body and a second passage formed in the extension,wherein the first passage is closed at the first side of the vent bodyand open at the second side of the vent body through an opening formedin the second side, and the second passage has an internal end open tothe first passage and an external end open to the atmosphere; wherebythe first side of the vent body may be inserted into the vent opening toprevent communication between the internal sump and the atmosphere, andthe second side of the vent body may be inserted into the vent openingto permit communication between the internal sump and the atmosphere.13. The vent of claim 12, wherein a portion of the first side and thesecond side each have a second diameter that is larger than the firstdiameter.
 14. The vent of claim 12, further comprising a membranedisposed in the internal passageway, wherein the membrane is airpermeable and water impermeable.
 15. The vent of claim 14, wherein themembrane is disposed in the first passage.
 16. The vent of claim 12,wherein the extension comprises a generally cylindrical side wallconnecting a first surface and a second surface, wherein the firstsurface contacts an external surface of the housing when the first sideof the vent body is inserted into the vent opening and the secondsurface contacts the external surface of the housing when the secondside of the vent body is inserted into the vent opening.
 17. The vent ofclaim 16, wherein a portion of the first side and the second side eachhave a second diameter that is larger than the first diameter.
 18. Thevent of claim 17, further comprising a membrane disposed in the internalpassageway, wherein the membrane is air permeable and water impermeable.19. The vent of claim 18, wherein the membrane is disposed in the firstpassage.